MonoGame: Fixing type or namespace name 'Xna' does not exist error

I wanted to play around with game development the other day, so I looked around for a decent .NET Game Framework and decided to go with the MonoGame framework. After installing it, I used the MonoGame OpenGL template to create a project in Visual Studio. Unfortunately, the build failed with the "The type or namespace name 'Xna' does not exist" error, but fortunately, the solution was straightforward and is the focus of this post.